docs: def normalize_headers(headers):
      """
      Convert useful headers to a normalized type and return in a new dict
  
      Only processes content-type, content-length, etag, and last-modified
      :param headers:
      :return:
      """
      for (k, v) in headers.items():
          headers.pop(k)
          headers[k.lower()] = v
  
      result = {}
      if 'content-length' in headers:
          result['content-length'] = headers['content-length']
      elif 'contentlength' in headers:
          result['content-length'] = headers['contentlength']
  
      if 'content-type' in headers:
          result['content-type'] = headers['content-type']
      elif 'contenttype' in headers:
          result['content-type'] = headers['contenttype']
  
      if 'last-modified' in headers:
          result['last-modified'] = headers['last-modified']
      elif 'lastmodified' in headers:
          result['last-modified'] = headers['lastmodified']
      else:
          result['last-modified'] = datetime.datetime.utcnow().strftime(RFC1123_TIME_FORMAT)
  
      # Normalize date
      if isinstance(result['last-modified'], datetime.datetime):
          result['last-modified'] = result['last-modified'].strftime(RFC1123_TIME_FORMAT)
  
      if 'ETag' in headers:
          result['etag'] = headers['etag'].strip('"')
      elif 'etag' in headers:
          result['etag'] = headers['etag'].strip('"')
  
      return result